This invention relates to a compositionally modulated metal structure. Compositionally modulated multilayers consist of layers of different metals or alloys. The most common methods for preparing such multilayers are physical deposition by sputtering or by molecular beam epitaxy. Such methods are not suited to the production of layers that are laterally modulated, that is, that are modulated in a direction other than perpendicular to the substrate surface with layer interfaces being roughly parallel to the substrate surface.
Electrodeposition of Co/Cu compositionally modulated multilayers with different sublayer thickness can be produced from a single bath as a function of different pulse potential and deposition charges. Multilayered Co/Cu deposits exhibit giant magnetoresistance (GMR) when the thickness of the bilayers is approximately a few nanometers (E. Gomez, A. Labarta, A. Llorente, and E. Valles, “Characterisation of cobalt/copper multilayers obtained by electrodeposition,” Surface and Coatings Technology vol 153 (2002) pp. 261-266). Galvanostatic electrodeposition has been used to produce NiCu/Cu multilayers by pulse plating from a sulfate/citrate electrolyte. GMR contributions were observed for most NiCu/Cu multilayers (E. Toth-Kadar, L. Peter, T. Becsei, J. Toth, L. Pogany, T. Tamoczi, P. Kamasa, I. Bakonyi, G. Lang, A. Cziraki, and W. Schwarzacher, “Preparation and Magnetoresistance Characteristics of Electrodeposited Ni—Cu Alloys and Ni—Cu/Cu Multilayers,” J. Electrochem Soc. vol. 149 (2000) pp. 3311-3318).
The preceding work produced multilayers with composition modulated in a vertical direction with respect to a substrate surface. For many applications, it may be advantageous to form a structure with lateral composition modulation. An example of such an application is a magnetoresistive sensor. A method for forming a magnetoresistive sensor has been patented that results in the spontaneous formation by self-assembly of a giant magnetoresistance multilayer structure of alternating stripes of ferromagnetic and nonferromagnetic metal that are stacked laterally on a special template layer. The template layer is a crystalline structure that has a two-fold uniaxial surface, i.e., one that is structurally invariant for rotation by 180 degrees (and only 180 degrees) about an axis (the symmetry axis) perpendicular to the surface plane. Alternating stripes of ferromagnetic metal (such as Co or Fe) and nonferromagnetic metal (such as Ag) become spontaneously arranged laterally on a (110) surface plane of body-centered-cubic Mo during co-deposition (D. E. Chambliss et al., U.S. Pat. No. 5,858,455).